In modern excavations to form tunnels, galleries and like elongates passages in subterranean formations, the use of tunneling machines is playing an ever increasing role. Such machines can comprise a head which is advanced in the desired direction against the face of the subterranean structure to be excavated and provided with excavating tools to break away the structure and form a detritus which is carried by conveyors of the machine rearwardly to be discharged out of the path of the head.
The excavating head is generally followed by a support structure which braces the machine so that the head can be advanced relative to the support which can then be drawn forwardly so that the next stage of advance of the head can be effected.
In addition, the machine can be provided with a shield which can surround the operating mechanism and can provide temporary support for the tunnel walls until finishing action, e.g. lining with concrete, grouting or the like, is undertaken. Generally the shield of the machine is advanced with the excavating head and comprises a cylindrical shell which lies close to the wall previously formed by the excavating head.
The shield can be coupled to the head for advance through the tunnel as it is formed. The shield can include at least two axially separated annular shell sections which are adjustably coupled together, and a so-called pressure ring can be provided. The two shell sections are bridged by a sealing member and the connecting elements may be distributed about the periphery of the shell sections, i.e. angularly equispaced therearound.
Machines of this type are known, for example, from German Pat. No. 24 31 652.
In general the shield constituted by one or more of such annular shell sections is advanced relative to the pressure ring through the excavated tunnel stretch by a cylinder arrangement.
The connecting elements described are generally screw-type members of a turnbuckle or equivalent configuration having nuts adjusting the effective lengths of these elements between two anchor points on the respective shell sections.
As a result, the screw-type members must be capable of resisting the forces which are generated as the shield is advanced, these forces being tension forces when the leading shield sections is advanced and the other section is drawn along.
The contacting elements allow a passive adjustment of the positions of the two shield sections relative to one another in terms of the angle between the respective axes of the shield sections by reducing the effective lengths of some of the connecting elements while increasing the effective lengths of others. An active adjustment is not possible and each adjustment of each element must be done by hand.
The mentioned angles between the axes of the shield sections are those which arise especially when the machine is advanced along an arcuate or curved path or indeed any path deviating from a straight line.
Where any adjustment of this angle is required, therefore a considerable amount of hand labor is involved.